Process of concentrating ore.



UNITED STATES PATENT OFFICE.

HENRY F. CAMPBELL, OF MELROSE, MASSACHUSETTS.

' PROCESS OF CONCENTRATING ORE.

SPECIFICATION forming part of Letters Patent No. 723,363, dated March24, 1903.

Application filed February 18, 1903 Serial No. 144,001; (No specimens-l7 To all whom it may concern.-

Be it known that I, HENRY F. CAMPBELL, a citizen of the United States,residing at Melrose, in the county of Middlesex and State ofMassachusetts, have invented a certain new.

and useful Process of Concentrating Ore, of which the following is aspecification.

My invention relates to the preparation of pyritiferous and other oresfor treatment by a magnetic machine or process and the concentration ofthe same by magnetic separation of. the valuable constituents from thewaste.

It consists in heating the ore to the extent and in the mannerhereinafter described.

My process is adapted for the treatment of a great variety of mineralores and deposits containing iron in any of its combinations, physicalor chemical. It is especially valuable in the treatment of such ores ascontain, among other constituents, iron sulfids carrying gold or silver,zinc-blendes, or copper pyrites. All ferruginous ores can be renderedmore valuable, and large bodies of mineral ores and deposits that havenot hitherto been worth the working can be made profitable by the use ofmy process.

Many attempts have been made to concentrate ores by magnetic separationand to prepare them therefor, and machines and processes have beendevised for those purposes, some of which have been patented; but thepractical results of these efforts have been unsatisfactory. In allinstances the treatment adapted to render the iron susceptible to theinfluence of magnetic attraction greatly impaired or destroyed thecommercial value of the zinc sulfids contained in the ore and alsorendered the zinc sulfids, silicates, and other so-called non-magneticmaterials in the ore sensitive to the influence of a magnetic field andprevented asatist'actory separation of theiron pyrites from them.Furthermore, the roasting process to which the ore was subjectedrequired a long time, and. careful observation was necessary todetermine when the ore was ready for removal from the furnace and toprevent it from oxidizing and fusing.

Heretofore it has been supposed that in order to render an iron sulfidmagnetic a considerable quantity of the sulfur' must be removed, atleast about one-half or what is known as the first atom, thus reducingthe pyrite to nearly or quite a pyrrhotite. To accomplish thisreduction, it is necessary to heat or roast the ore for a considerablepethe ore and the zinc sulfid left unimpaired,-

for smelting and commercial purposes. In zinciferous ores bearing leadthe lead may be removed by water concentration in the usual way, eitherbefore or after the treatment by my process.

My process is also valuable in the treatment of ferruginous manganeseores. I have found that by a brief heating in many cases the greaterpart of the iron may be-removed from the manganese. I further find thatbya more prolonged heating I am able to remove both the'iron andmanganese from the silica and other constituents.

Prior to myinvention it was unknown that the action of heat upon orecontaining zinc sulfids, silicates, and other non-magnetic materials wassuch as to cause the non-magnetic materials to be removed from the oreby magnetic attraction in the process of magnetic separation owing tomagnetic sensibility be-.

the ore were rendered susceptible to removal from the mass by magneticforce. I have discovered that iron pyrites can be rendered magnetic bythe action of heat without the removal of an appreciable amount ofsulfur and that the magnetic effect is chiefly due to the direct actionof the heat upon the iron pyrites and not that it is caused by theremoval of the sulfur. The removal of the sulfur in the prior methods oftreating ore by roasting to render it magnetic was an incident of theprolonged exposure to heat, but was not necessary to magnetize the ironpyrites, as it has been erroneously supposed. I find that if ironpyrites are subjected to the action of heat for the brief space of oneminute, or even less, they are rendered magnetic, and that it is notalways necessary to heat the ore to redness in order to suitably prepareit for separation by a magnetic machine or process. If less than a redheat is employed, a longer exposure is required. The degree of heat mustbe considered in determining the length of exposure of the ore thereto.The degree of heat and length of exposure should be adequate only tomagnetize the iron without sensitizing the zinc, silicates, or othernon-magnetic materials and without removing an appreciable amount ofsulfur. Different ores of this character vary somewhat in therequirements to render them sufliciently magnetic for the best resultsin the separating process; but exposure to red heat for five minutes orless is all that is required for the most refractory ores to give thebest results. Less than fivc minutes exposure to red heat in an ordinaryrotary furnace under the usually-prevailing conditions renders themajority of ores sufficiently magnetic to prepare them for commercialseparation. This is not attended with the removal of sufficient sulfurto impair the commercial value of the zinc sulfids.

I have discovered thatin the magnetic separation of ores containingzinc, silicates, and other waste materials if subjected to a high degreeand long duration of heat, such as has been heretofore the practice,alarge amount of the zinc, silicates, and waste willbe lifted out by themagnets and mingled with the concentrates by reason of the prolongedheatimparting magnetic sensibility to such materials or to infinitesimalparticles of some paramagnetic matter with which they are associated. Ihave discovered that when these materials are subjected to a brief redheat of but a few minutes, which is sufficient to magnetize the iron,they are not affected so as to be lifted out of the mass of ore by themagnets. My discoveries enable me to treat ores containing non-magneticiron and copper pyrites combined with zinc sulfids, silicates, and otherwaste materials, so as to remove all the iron from the mass that can beprofitably taken out by magnetic attraction, and to exclude essentiallyall the zinc, silicates, and other waste materials. In workingzinciferous ores recess 1 am thereby enabled to get a valuable zincproduct, removing practically all the iron, and to get a valuableconcentrate in the product lifted out by the magnets.

In the practice of my invention the ore is first pulverized orcomminuted from twenty to thirty mesh and then charged into any of thewell-known furnaces for roasting ore and subjected to heat under theusually-prevailing conditions. I prefer to use a cylindrical rotaryfurnace having the fire-box at one end and receiving the ore at theother, similar to the White Howell pattern, for the purpose of agitatingthe ore and heating it uniformly at the same time. It is desirable insome instances to give the furnace a sharp pitch or angle ofinclination, so that the ore will feed or drop quickly through it, andto construct the interior of the furnace without the partitions orseptums which are ordinarily employed, so as to avoid obstructions tothe free passage of the ore. The ore in passing through the furnace isexposed to heat for a predetermined length of time. This is ascertainedby heating several sample lots or specimens of a given ore to a red heatfor different periods of time, ranging from a few seconds to fiveminutes, and then subjecting them to the action of a magnetic separatorand assaying the products for the purpose of determining which specimenaffords the best results with respect to the purity of concentrateproducedthat is to say, I submit a specimen of crushed or pulverized oreto a quick blast of red heat by passing it through the furnace asrapidly as possible, occupying but a few seconds of time, and thenrunning it through the magnetic separating-machine and assaying theproducts. This brief action of heat will magnetize the iron pyrites tosome extent in any ore and sufficiently in some ores so that all theiron pyrites, together with the gold, silver, and copper with which itis combined, will be removed from the mass by the magnetic separatorwithout removing any appre ciable amount of the silicious andnon-magnetic materials. The products are then assayed, and if found thatall the iron pyrites are not removed from the mass I subject anotherspecimen of the ore to the action of the furnace at the same heat for aslightly-longer time and in turn run it through the magnetic separatorand assay the products, as before.

This operation is repeated on difierent specimens of a giv'en ore untilthe length of time is ascertained which is required for heating the oreto enable the separating-machine to remove the largest percentage of theiron pyrites essentially free from silicious and other waste materials.I find that after an exposure of any ore to red heat for a period offive minutes or less, generally not more than three minutes, practicallyall the iron pyrites will be removed by the magnetic separating processand that no appreciable amount of sulfur will be removed from thezinc-blends contained in the ore, and the silicates and other materialsthat become sensitized to the magnet by prolonged heating are notaffected by the influence of the magnetic field.

For the purpose of illustrating I take a sample of ore which contains,say, thirty-four per cent. of iron pyrites bearing gold or silver,thirty-eight per cent. of zinc sulfid, and twenty-eight per cent. oflead, silicates, and waste materials. I pulverize it to twenty mesh andsubject it to abarely-perceptible red heat for thirty seconds. Then Icool it speedily and run it through amagnetic separatingmachine. Theproducts are assayed, and if, say, from thirty to thirty-three per cent.of the ore removed by the magnetic action is iron pyrites bearing goldor silver essentially free from silicates and other non-magnetics andthe residue of the ore shows but a small trace of iron pyrites theoperation is regarded as successful, and the bulk of the ore is subjected to the same heat for the same time. If a substantial portion ofthe iron pyrites remains with the silicates and non-magnetics,

I subject the ore to the same degree of heat for a slightlylonger timeand repeat the operation of magnetic separating and assaying theproducts until the desired separa tion is attained. It may be necessaryto make several tests for difierent lengths of time, not exceeding fiveminutes to attain the best results. It will be found as a result of alltests that the zinc sulfid will have parted with scarcely any of itssulfur, not enough to impair at all its commercial value. If theproducts of any test should reveal a considerable quantity of zinc,silicates, or other socalled non -magnetics, mingled with the ironpyrites removed by the magnets, the ore should of course be subjected toheat for a less period of time.

By an intelligent use of my process in treating pyritiferous oreapractically perfect separation of the iron pyritesfrom the otherconstituents can be attained, and where zincblende is present it willretain, essentially, all its sulfur and not be impaired for smelting andcommercial purposes. Having ascertained the length of time and degree ofheat required to attain the best results with a given ore, the revolvingspeed of the furnace and its angle of inclination are adjusted to causethe ore to pass through it in that space of time and the furnace isfired to the requisite degree of heat. It is impracticable to adjust thespeed and inclination of the furnace so as to'fix absolutely the time ofpassage of the ore through it, but it can be approximately done andsufficiently so for all practical purposes. N 0 other test than I havedescribed is required to determine when the ore'should be dischargedfrom the furnace. No examination of the ore is needed during the heatingprocess, and no care is required to prevent oxidizing or fusing of thematerials, a's heretofore, because the exposure to heat in my process isnever sufficient in case of .the most refractory ore to incur any dangerof these evils. When the ore is discharged from the furnace, it isquickly cooled, preferably by artificial means. The time consumed incooling the ore must be taken into consideration in estimating theduration of time to which it is exposed to heat. If it is allowed tocool slowly, it is of course thereby exposed to heat for a longer periodof time than when cooled quickly. After cooling the ore it is passedthrough a magnetic separating-machine, the one preferred being thesocalled Campbell machine invented by me.

I desire to emphasize the marked distinction between my process and theold methods, which resides in the brief subjection to heat. Inpracticing my process I retain substantially all the sulfur in the ore,while in the former methods it was customary to eliminate a substantialportion ofsulfur without fusing the particles of ore. It was a delicateprocess to follow the operation so closely as to attain this result.Experience and skill were required to do it. In properly practicing myinvention it is impossible to fuse the particles of ore in that degreeand duration of heat required to treat the most refractory ore. Noattention whatever is required in that respect. The length of time theore is to remain in or occupy in passing through the furnace ispredetermined, and when the time expires it is discharged from thefurnace, having required no inspection or test during the heatingprocess. If the ore treated con tain iron and zinc sulfids, the iron isremoved by magnetic attraction and delivered into one receptacle and thezinc sulfid and waste materials are discharged into another. The zincsulfid has parted with no appreciable amount of sulfur and is unimpairedfor smelting purposes. If the zinciferous ore contains gold, silver, orcopper, nearly all the gold and copper and a large percentage of thesilver are removed with the iron pyrites, and the expense of smeltingthe same is greatly reduced by reason of the absence of zinc. If the oreconsists of iron pyrites bearing values combined with silicious andother waste materials, the iron and nearly all-the valuable constituentsare removed without carrying with them any appreciable portion of thewaste, thus saving the cost of transportation of the waste and renderingthe valuable portions of the ore less expensive to treat at the smelter,for not only is it an expense to handle the waste materials at thesmelter, but an additional charge is made or. penalty imposed forsmelting concentrates in proportion to the percentage of waste whichthey contain. There are some ores in which the silicates are sosensitive that essentially all cannotbe excluded from the iron; but inthese instances a large percentage can be excluded by my process thatwould otherwise be removed with the iron.. In an ore carrying only ironpyrites and silicious and other waste materials the pyrites may beseparated with butslight loss of sulfur,th us rendering them moreavailable for the manufacture of sulfuric acid or metallic sulfur.

The advantages of my process over former methods in addition to making abetter separation of the valuable portion of the ore from the wastematerials and not impairing the commercial value of some of theconstituents consist in a saving of fuel and time, less skill inconducting the work, and in avoiding dust during the separating process.

The gist of my invention resides in the discoveries that non-magneticiron sulfids in mineral ores may be rendered magnetic by heat withoutremoving the sulfur from the ore to any material extent; that thesilicious and other non-magnetic materials of the ore are sensitized ormade susceptible to the influence of a magnetic field by heating orroasting the ore to the extent employed in earlier experiments ofreducing it essentially to a pyrrhotite and are not materiallysensitized by the degree and duration of heat which I have discoveredare sufficient to magnetize the iron pyrites.

My invention is not limited to the use of any particular construction offurnace or means of magnetic separating or method of determining thelength of time to subject the ore to heat. Various forms of furnaces,different means of magnetic separating and methods of determining thedegree and duration of heat for a given ore may be employed inpracticing my invention than those described andwould be within thescope thereof.

Although I have designated as magnetic the electrical efiect employed byme as the means for separating the ore, any electrical or polarizinginfluence that may be utilized for diverting the constituents of the oreinto dilferent channels when used in conjunction with my describedprocess of preparing the ore therefor is comprehended by my inventionand is to be understood as included within the means for separating theore wherever and in whatever terms they are mentioned herein.

What I claim, and desire to secure by Letters Patent, is

1. The hereinbefore-described process of concentrating ferruginous orescontaining sulfids, which consists in heating the mate-- rial for abrief time sufficiently to render portions thereof responsivetoelectrical influences without the removal of a substantial amount ofany constituent other than water, and subjecting the material to suchinfluences for the removal of the portions of the material renderedresponsive.

2. The hereinbefore-described process of concentrating ferruginous orecontaining silicious or other waste materials, which consists in heatingthe same for a brief time sufficiently to render portions thereofresponsive to electrical influences without the removal of a substantialamount of any constituent other than water, and then subjecting thematerial to such influences for the removal of theportions ofthematerial rendered responsive, and leaving in the residue substantialquantities of silicious or other waste materials susceptible of beingremoved by such influences upon greater exposure to heat.

3. The hereinbefore-described process of concentrating ferruginous orecontaining zinc sulfids or other non-magnetic values, which consists insubjecting the same to the action of heat for a brief time sufiicient tomagnetize the principal iron constituents of the ore, but insufficientto cause the removal of a substantial amount of the constituents of theore other than water, then magnetically removing the said ironconstituents and leaving in the residue substantial quantities of zincsulfids or other non-magnetic values susceptible of being magneticallyremoved from the ore upon greater exposure to heat.

4. The hereinbefore-described process of concentrating ferruginous orecontaining silicious or other Waste materials which consists insubjecting the same to the action of heat for a brief time suflicient tomagnetize the principal iron constituents of the ore but insufficient tocause the removal of a substantial amount of the constituents of the oreother than water, then magnetically removing the said iron constituentsand leaving in the residue substantial quantities of silicious or otherwaste materials susceptible of being magnetically removed from the oreupon greater exposure to heat.

5. The hereinbeforedescribed process of concentrating pyritiferous orewhich consists in subjecting the same to sufficient heat to magnetizethe iron pyrites for a period of time insufficient to drive off anysubstantial amount of sulfur and then magnetically separating thepyrites from the mass, while they retain practically all the originalquantity of sulfur.

6. The hereinbefore-described process of concentrating pyritiferous orecontainingzinc sulfids or other non-magnetic values, which consists insubjecting the same to sufficient heat to magnetize the pyrites for aperiod of time insufficient to drive off any substantial amount ofsulfur and then magnetically separating the pyrites from the mass whilethey retain practically all the original quantity of sulfur and leavingin the residue substantial quantities of zinc sulfids or othernon-magnetic values susceptible of being magnetically removed from theore upon greater exposure to heat.

7. The hereinbefore-described process of.

tities of silicious or other waste materials susceptible of beingmagnetically removed from the ore upon greater exposure to heat.

8. The process of concentrating ferruginous ore which consists insubjecting the same to the action of red heat for a period not exceedingfive minutes, and then magnetically separating the iron constituentsfrom the ore.

9. The process of concentrating pyritiferous ore containing zinc sulfidsor other nonmagnetic values, which consists in subjecting the same tothe action of red heat for a period not exceeding five minutes, and thenmagnetically separating the pyrites from the mass and leavingsubstantial quantities of zinc sulfids or other non-magnetic values inthe residue, susceptible of being magnetically removed from the ore upongreater exposure to heat.

10. The-process of concentrating pyritiferous ore containing siliciousor other waste materials, which consists in subjecting the same to theaction of red heat for a period ous orecontaining zinc sulfids or othernonmagnetic values, which consists in subjecting the same to the actionof red heat for a period not exceeding five minutes, and thenmagnetically separating the pyrites from the mass and leavingsubstantial quantities of zinc sulfids, silicious and other wastematerials in the residue, susceptible of being magnetically removed fromthe ore upon greater exposure to heat.

In testimony whereof I hereunto set my hand this 6th day of February, A.D. 1903. HENRY F. CAMPBELL. Witnesses:

CHAS. F. PERKINS, A. G. SULLIVAN.

